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Thread: Minimum Ductbank Cover

  1. #1
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    Minimum Ductbank Cover

    Does the NEC address minimum coverage requirements for low voltage concrete-encased conduit? Table 300.5 seems to apply only to direct-buried conduits, and Figure 310.60 applies to medium voltage conductors. I have a 480V ductbank that was designed for 18" minimum coverage, but field conditions necessitate a shallower installation. I'm trying to determine if there are Code implications. . . .

  2. #2
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    Quote Originally Posted by msteiner
    Does the NEC address minimum coverage requirements for low voltage concrete-encased conduit? Table 300.5 seems to apply only to direct-buried conduits, and Figure 310.60 applies to medium voltage conductors. I have a 480V ductbank that was designed for 18" minimum coverage, but field conditions necessitate a shallower installation. I'm trying to determine if there are Code implications. . . .
    T300.5
    Under minimum of 102-mm (4-in.) thick concrete exterior slab with no vehicular traffic and the slab extending not less than 152 mm (6 in.) beyond the underground installation
    If your duct bank meets these conditions and or you pour a slab over the bank then your looking at 4" cover IMO.

  3. #3
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    Chris - I guess I buy the argument that the concrete in the ductbank could consitute the 4" thick slab required by T300.5, but I wouldn't think an additional slab over top of the ductbank would be required. If I understand you correctly, that seems to be what you're suggesting.

  4. #4
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    Quote Originally Posted by msteiner
    Chris - I guess I buy the argument that the concrete in the ductbank could consitute the 4" thick slab required by T300.5, but I wouldn't think an additional slab over top of the ductbank would be required. If I understand you correctly, that seems to be what you're suggesting.
    Is a duct bank a slab?

    Under minimum of 102-mm (4-in.) thick concrete exterior slab
    I can tell you I don't know of any inspector around here that would have a problem if I showed him the job site conditions and detail of the duct bank.

    Your OP didn't say if these were service laterals or feeders with OCP. That could make a difference.

  5. #5
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    Question

    This also depends on how thick the concrete is on the top of the duct bank. I have seen some pretty thin pours for some reason. :-?
    Charlie Eldridge, Indianapolis, Utility Power Guy
    Responses based on the 2011 NEC, unless stated otherwise.

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